Latch and Flip-Flop Explained | Difference between the Latch and Flip-Flop
Summary
TLDRThis video from the 'All About Electronics' YouTube channel explores basic memory elements in sequential circuits, focusing on Latches and Flip-Flops. It explains that both can store one bit of information and are known as Bistable Multivibrators. The video distinguishes between Transparent Latches, which respond immediately to input changes, and Gated Latches that respond based on control input. It also contrasts these with Flip-Flops, which are Edge Triggered and respond only at clock transitions, highlighting their use in synchronous circuits.
Takeaways
- š The video discusses basic memory elements used in sequential circuits, focusing on Latches and Flip-Flops.
- š Both Latches and Flip-Flops can store one bit of information, having two stable states, and are thus known as Bistable Multivibrators.
- š A Latch responds to input level changes immediately, making it an Asynchronous type of memory element.
- šļøāšØļø Transparent Latches change their output state immediately with input changes, while Gated Latches require an enable input to be high to respond to input changes.
- š Gated Latches can act as Synchronous memory elements when a periodic clock signal is applied to the enable input, responding to input changes only when the clock signal is high.
- š The timing diagram illustrates how a Gated Latch behaves during on and off times of the clock signal, showing its level sensitivity.
- š Flip-Flops, unlike Latches, are Edge Triggered Memory Elements, responding to input changes only at the clock transition.
- ā« Positive Edge Triggered Flip-Flops respond to input changes at the Rising Edge of the clock signal, while Negative Edge Triggered Flip-Flops respond at the Falling Edge.
- š The output of a Flip-Flop retains its state until the next clock transition, regardless of input changes in between.
- š Gated Latches and Flip-Flops respond differently to the same input and clock signal due to their sensitivity to level changes versus edge transitions.
- š ļø Latches and Flip-Flops are implemented using LOGIC gates, and the video promises to cover their design in upcoming videos.
Q & A
What are the basic memory elements used in sequential circuits?
-The basic memory elements used in sequential circuits are Latches and Flip-Flops.
What is the primary function of a memory element in sequential circuits?
-The primary function of a memory element in sequential circuits is to store one bit of information, which can be either zero or 1.
What is another name for Latches and Flip-Flops due to their two stable states?
-Latches and Flip-Flops are also known as Bistable Multivibrators due to their two stable states.
How does a Latch respond to input level changes?
-A Latch responds to input level changes immediately, making it an Asynchronous type of memory element.
What is a Transparent Latch?
-A Transparent Latch is a type of Latch that immediately responds to the change in the input level.
What is a Gated Latch and how does it differ from a Transparent Latch?
-A Gated Latch is a Latch that becomes transparent based on the control input. Unlike a Transparent Latch, it only responds to input changes when the enable input is high.
How can a Gated Latch be used as a Synchronous memory element?
-A Gated Latch can be used as a Synchronous memory element by applying a periodic clock signal to its enable input. It will respond to the input when the clock signal is high and retain its previous state when the clock signal is low.
What is the difference between a Latch and a Flip-Flop in terms of their sensitivity to input changes?
-A Latch is a Level Sensitive Memory Element, responding to the level of the input signal, while a Flip-Flop is an Edge Triggered Memory Element, responding to the transitions (edges) of the clock signal.
What are the two types of Edge Triggered Flip-Flops based on their response to clock signal transitions?
-The two types of Edge Triggered Flip-Flops are Positive Edge Triggered Flip-Flops, which respond to the Rising Edge of the clock signal, and Negative Edge Triggered Flip-Flops, which respond to the Falling Edge of the clock signal.
How can a Gated Latch be modified to function as a Flip-Flop?
-A Gated Latch can be modified to function as a Flip-Flop by adding a clock transition circuit, which allows it to respond to the clock signal transitions rather than the clock signal level.
How are Latches and Flip-Flops implemented in practice?
-Latches and Flip-Flops are implemented using LOGIC gates.
Outlines
š Introduction to Memory Elements in Sequential Circuits
This paragraph introduces the fundamental memory elements, Latch and Flip-Flop, used in sequential circuits. It explains that these elements can store one bit of information, making them essential building blocks. Latches respond immediately to input level changes, while Flip-Flops require a clock signal to update their state. The paragraph also distinguishes between Transparent Latches, which always respond to input changes, and Gated Latches, which only respond when an enable input is high. The concept of a clock signal turning a Gated Latch into a Synchronous memory element is introduced, highlighting the importance of clock signals in controlling memory element behavior.
š Understanding Latch and Flip-Flop Behavior with Timing Diagrams
This paragraph delves deeper into the behavior of Latches and Flip-Flops, particularly focusing on their response to clock signals. It explains that Flip-Flops can be either Positive Edge Triggered or Negative Edge Triggered, responding to the rising or falling edge of a clock signal, respectively. The paragraph uses timing diagrams to illustrate how a Gated Latch behaves as a Level Sensitive Memory Element when a periodic clock pulse is applied to its enable input, becoming transparent during the high clock signal and retaining its state during the low signal. In contrast, Flip-Flops are described as Edge Triggered Memory Elements, responding only at the clock transition. The paragraph concludes by noting that while Flip-Flops are typically used in Synchronous circuits, a Gated Latch can be modified to function as a Flip-Flop, setting the stage for further exploration in future videos.
Mindmap
Keywords
š”Memory Elements
š”Sequential Circuits
š”Latch
š”Flip-Flop
š”Bistable Multivibrator
š”Transparent Latch
š”Gated Latch
š”Clock Signal
š”Edge Triggered
š”Logic Gates
š”Synchronous Circuits
Highlights
Introduction to basic memory elements used in sequential circuits.
Memory elements are essential building blocks of sequential circuits.
Two types of memory elements: Latch and Flip-Flop.
Both Latch and Flip-Flop can store one bit of information.
Latch and Flip-Flop are also known as Bistable Multivibrators.
Latch responds to input level change immediately.
Transparent Latch is an Asynchronous type of memory element.
Gated Latch becomes transparent based on control input.
Gated Latch can be used as a Synchronous memory element with a periodic clock signal.
Gated Latch is sensitive to the clock signal level.
Flip-Flop is an Edge Triggered Memory Element.
Flip-Flop can respond to input at the Rising or Falling Edge of the clock signal.
Positive Edge Triggered Flip-Flop follows input at the Rising Edge.
Negative Edge Triggered Flip-Flop follows input at the Falling Edge.
Gated Latch and Flip-Flop respond differently to the same input and clock signal.
Flip-Flop is typically used as the Memory element in Synchronous circuits.
Gated Latch can be modified to function as a Flip-Flop.
Latches and Flip-Flops are implemented using LOGIC gates.
Upcoming videos will cover the design of transparent Latch and gated latch using LOGIC gates.
Transcripts
Hey, friends welcome to the YouTube channelĀ ALL ABOUT ELECTRONICS. So in this video,Ā Ā
we will learn about the basic memory elements.Ā Which are used in the sequential circuits.Ā Ā
So in the previous video, we have seen that, thisĀ memory element is very essential and the basicĀ Ā
building block of any sequential circuits.Ā So basically there are two types of memoryĀ Ā
elements, which are used in the sequentialĀ circuits. That is Latch and the Flip-Flop.Ā Ā
Well, both the memory elements are able to storeĀ one bit of information. That means, their outputĀ Ā
can be either zero or 1. And since they have theĀ 2 stable states, so they are also known as theĀ Ā
Bistable Multivibrator. So in this video, letĀ us understand what is Latch and Flip-Flop,Ā Ā
and what is the basic difference between two ofĀ them. So first of all let's start with the Latch.Ā Ā
So this Latch responds to the input level changeĀ immediately. For example, let's say initially theĀ Ā
input of this latch is equal to 1. And based onĀ that the stored value in the Latch is equal to 1.Ā Ā
Now suddenly, if the input level changes to 0 thenĀ the Latch will also immediately respond to thatĀ Ā
input level change. And based on that change, itĀ will also change the output stage. So basically,Ā Ā
it is the Asynchronous type of memory element. SoĀ this type of Latch, which immediately responds toĀ Ā
the change in the input, are called TransparentĀ Latch. Now there is another type of Latch whichĀ Ā
becomes transparent, based on the control input.Ā So this Latches are known as the Gated Latch.Ā Ā
So as you can see, this Gated Latch also hasĀ enable input. So when this enable input is high,Ā Ā
then this Latch is transparent to the input.Ā That means, when this enable input is high,Ā Ā
then the Latch responds to the change in the inputĀ immediately. And when this enable input is low,Ā Ā
then even if the input changes, then it does notĀ respond to that input change. And in that case,Ā Ā
it retains its previous state. Now, when we applyĀ the periodic clock signal to this enable input,Ā Ā
then the same Gated Latch can be used as theĀ Synchronous memory element. Because now this latchĀ Ā
will respond to the input, when the clock signalĀ is high. And it will remain in its previous state,Ā Ā
when this clock signal is low. So as you can see,Ā basically it is sensitive to the clock signalĀ Ā
level. But during this on time of the clock, ifĀ the input level changes, then it will respond toĀ Ā
that change immediately. So let us understand theĀ working of this Gated Latch with the help of theĀ Ā
timing diagram. So let's see here, we have oneĀ Gated Latch and the clock signal is applied asĀ Ā
the enable input. So here, the signal which isĀ shown in the blue color is our clock signal. AndĀ Ā
that signal is applied at the enable input. So asĀ you know this Gated Latch will become transparent,Ā Ā
when the clock signal is high. Or in other words,Ā when this enable input is high. So as you can see,Ā Ā
during the on time of this clock signal, whenĀ the enable input is high, then the outputĀ Ā
of the Latch is same as the input signal. AndĀ after that, when this enable input becomes low,Ā Ā
then even if the input signal changes, then alsoĀ this Latch will not respond to that input change.Ā Ā
And as you can see, it is retaining its previousĀ state. So in this case, during the off time itĀ Ā
will remain zero. Now once again, during theĀ on time of the clock when the enable inputĀ Ā
becomes high, then once again the output willĀ follow the input signal. So as you can see,Ā Ā
during this time, this output is following theĀ input signal. And once again, during the off timeĀ Ā
of the clock signal, it will retain its previousĀ state. So as you can see, during this off time,Ā Ā
the input is going from high to low. But stillĀ this Latch will not respond to that input change.Ā Ā
And it will retain its previous state. Now onceĀ again, it will become transparent to the input,Ā Ā
when the clock signal is high. Or in otherĀ words, once again when the enable input is high.Ā Ā
So at that time since the input isĀ low, so the output will also becomeĀ Ā
low. So this is the output of this Gated Latch.Ā And as you can see, when this periodic clock pulseĀ Ā
is applied at the enable input, then this GatedĀ Latch will become Level Sensitive Memory Element.Ā Ā
That means, it will become transparent, whenĀ this clock signal is high. On the other end,Ā Ā
if you see the Flip-Flop then, it also hasĀ clock input. And it responds to the input,Ā Ā
only at the clock transition. That means, theĀ Flip-Flop is the Edge Triggered Memory Element.Ā Ā
On the other end, if you see the Latch,Ā then it is the Level Triggered MemoryĀ Ā
Element. Now this Flip-Flop can respondĀ to the input, either at the Rising Edge,Ā Ā
or the Falling Edge of the clock signal. So ifĀ it responds to the input, at the Rising Edge,Ā Ā
then it is called as the Positive Edge TriggeredĀ Flip-Flop. On the other end, if it responds to theĀ Ā
input at the Falling Edge of the clock, then itĀ is called as the Negatives Edge Triggered Flip-Flop.Ā Ā
So through the timing diagram, let us understand,Ā how this is Edge triggered Flip-Flop behaves to theĀ Ā
input level changes. And first let's take theĀ case of the Positive Edge Triggered Flip-Flop.Ā Ā
So here, the same signal, which we have applied toĀ the Gated Latch, is also applied to the Flip-Flop.Ā Ā
And this signal which is shown in the blue color,Ā is our clock signal. So since the Flip-Flop is theĀ Ā
Edge Triggered Flip-Flop, so it will respondĀ to the input at the Rising Edge of the clock.Ā Ā
And here, we are assuming that at the clockĀ transition the Flip-Flop follows the input signal.Ā Ā
That means, at the clock transition, if the inputĀ is high, then the output of the Flip-Flop is alsoĀ Ā
high. And if the input is low, then the output ofĀ the Flip-Flop will also become low. So based onĀ Ā
that assumption, let us see what will be theĀ output of this Flip-Flop. So as you can see,Ā Ā
at the first Rising Edge, the input is high.Ā That means, the output will also become high.Ā Ā
But, now the Flip-Flop will respond to theĀ input, at the next Rising Edge. And till that,Ā Ā
it will retain its previous state. That meansĀ in this case, until the next Rising Edge,Ā Ā
it will remain high. That means up to thisĀ point, the output of the Flip-Flop will remainĀ Ā
high. Now once again, at the next Rising Edge,Ā the input is once again high. That means duringĀ Ā
the next clock transition also the outputĀ will remain high. And it will remain high,Ā Ā
until the next clock transition. So in between,Ā even if the input level changes, then also it willĀ Ā
not respond to that input level change. So now atĀ the next clock transition, since the input becomesĀ Ā
low, so the output will also become low. And itĀ will remain low, till the next clock transition.Ā Ā
So as you can see, this is the output ofĀ this Positive Edge Triggered Flip-Flop.Ā Ā
Similarly, for the same inputs let's see theĀ output of this Negative Edge Triggered Flip-Flop.Ā Ā
So this Negative Edge Triggered Flip-Flop,Ā will respond to the input at the Falling Edge.Ā Ā
So till the first Falling Edge, the output ofĀ the Flip-Flop will remain zero. Now at the firstĀ Ā
Falling Edge, if you see then the input is low.Ā That means the output of the Flip-Flop will alsoĀ Ā
remain low. And it will remain in this state,Ā until the next Falling Edge. Now once againĀ Ā
at the next Falling Edge if you see, then theĀ input becomes high. So since the input is high,Ā Ā
so the output will also become high. And it willĀ remain in this state, until the next Falling Edge.Ā Ā
So in between the two Falling Edges, even if theĀ input level changes, then also this Flip-FlopĀ Ā
will not respond to that input level change.Ā And at the next clock transition if you see,Ā Ā
then the input becomes low. That means now, theĀ output of the Flip-Flop, will also become low.Ā Ā
So overall, this is the output of this NegativeĀ Edge Triggered Flip-Flop. So as you can see,Ā Ā
for the same input and the clock signal the GatedĀ Latch and the Flip-Flop responds differently.Ā Ā
Because this Flip-Flop is the Edge sensitive, butĀ the Latch is the level sensitive. So typically,Ā Ā
in the Synchronous circuits, this Flip-Flop isĀ used as the Memory element. And in fact with theĀ Ā
little modification, the Gated Latch can beĀ used itself as the Flip-Flop. For example ifĀ Ā
we add the clock transition circuit to this GatedĀ Latch, then the same can be used as the Flip-Flop.Ā Ā
So in the upcoming videos, we will also learnĀ about that. But first it is good to know theĀ Ā
basic design of the Latch. So this Latches andĀ Flip-Flops are implemented with the help of theĀ Ā
LOGIC gates. So in the next video, we will learnĀ that, how to design the transparent Latch as wellĀ Ā
as the gated latch with the help of the LOGICĀ gates. But I hope in this video you understoodĀ Ā
what is Latch and Flip-Flop. And what is the basicĀ difference between the Latch and the Flip-Flop.Ā Ā
So if you have any question or suggestion, then doĀ let me know here in the comment section below. IfĀ Ā
you like this video, hit the like button andĀ subscribe the channel for more such videos.
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